Yamaha 250SHO dying after long idles

Flysooner9

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Last two times out after long idle in and out of a no wake zone my 250 SHO dies. When I pump the fuel bulb it’s completely empty. After re priming the line it starts right back up and runs fine once your above idle Rpm’s

my first guess is a failing low pressure pump? Maybe clogged filters?
Runs perfect all day at high rpm’s.
 
Isolate the problem to either before bulb or after the priming bulb. Run a fuel line from a gas can and see if problem occurs, if it does it’s after bulb, if it doesn’t it’s tank or line before bulb. Once that is known tackle the suspect areas. I agree with you it’s probably a pump issue. However it could be a tiny hole in fuel line that closes up under a heavy vacuum and then opens under light vacuum (idle) and the resultant fuel starvation.
 
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Sounds like a small air leak in the line, connections or bulb. Possible tank vent issue too.
 
I would think if it’s a vacuum problem the priming bulb would be collapsed or nearly so. Of course it certainly is easy to open fuel cap and see if a inrush of air happens. I hope once this is figured out, you share.
 
Last two times out after long idle in and out of a no wake zone my 250 SHO dies. When I pump the fuel bulb it’s completely empty. After re priming the line it starts right back up and runs fine once your above idle Rpm’s

my first guess is a failing low pressure pump? Maybe clogged filters?
Runs perfect all day at high rpm’s.
Consider adding a can or two of "Seafoam" I use it regularly, cheaper than getting the motor serviced.
 
Not a vacuum problem as there is zero sound when I open the fuel cap. Planning to do filters next then if that doesn’t fix it fuel lines. If that doesn’t do it I’ll do the low rpm pump.
 
I would try replacing the primer bulb before the low pressure pump. If it's collapsing the bulb, would seem to me that the pump was working.
 
If it’s the original gas bulb, it doesn’t hurt to replace it. I’ve seen them fail too many times without any indicators. I replaced all my gas lines after 6 years. Same with my battery cables as they get soaked every outing in salt water. Call it Preventive Maintenance which is always smart to do. Good Luck & keep us posted.
 
Still working this problem

Will run fine the first 30-60 minutes. After that if you have a pro longed run at idle motor will cough then die. Will not restart unless you re prime the bulb. Will start but then will shortly try to die again unless you can get it over 4,000 rpm quick then it’ll run fine above that rpm for any amount of time. However once you bring it back to idle it’ll die again after a few minutes.

So far I have:
Changed prime line and bulb
Changed fuel line from tank to water separator
Changed large blue filter
Changed low pressure fuel pump.

I also have tried running with fuel cap off to check for a venting issue? Same result

I need to change the onboard filter still but can’t imagine that would be it since it only starts doing it after the first 60 min or so.

Really starting to run out of ideas. Anyone have any help before I give up and probably go spend thousands at the dealer?
 
Get a 5-10 gal gas can and run fuel from that. It will tell you if it’s in boat fuel tank or not. You may have that gas can if you mow your yard so it’s a cheap and easy check. Let us know.
 
Get a 5-10 gal gas can and run fuel from that. It will tell you if it’s in boat fuel tank or not. You may have that gas can if you mow your yard so it’s a cheap and easy check. Let us know.
I was thinking same thing, even a portable 6 gallon boat fuel tank. I was thinking fuel pickup issue inside tank.
 
I was thinking same thing, even a portable 6 gallon boat fuel tank. I was thinking fuel pickup issue inside tank.
I’m still thinking a very small hole in fuel line that at idle will suck air and when high demand for fuel (at speed) it closes.
 
I’m still thinking a very small hole in fuel line that at idle will suck air and when high demand for fuel (at speed) it closes.
Didn't he say above that he replaced the fuel line among other things ?
 
Not in tank. We can eliminate tank and any fuel issue in it, if we bypass it.
 
Air leaks should all be eliminated before replacing a bunch of expensive parts. Filter gaskets, fuel lines, incorrectly replaced parts (upside down fuel bulbs, etc.) are all inexpensive albeit time consuming things to check

As others have noted if your bulb is not flat then a blockage or venting issue does not seem to be the cause.

Another thing to check although it's usually a high RPM thing is the VST. A couple filters in that may be dirty/clogged, which even if it doesn't solve the original problem is still a maintenance item that eventually needs to be completed.

Lastly it could be an intermittent electrical issue if the idling is creating heat and expansion somehow works a ground wire loose or solenoid or relay fails. That is on the very low probability end of things but something to add to the list.

Good luck tracking this sucker down!
 
We have our 1st outboard, a Mercury 150 4 stroke after having an I/O for 12 yrs. I don't remember ever seeing a primer bulb on ours???
 
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